Patent GB-1366402-A (GB)
Title: Inhibit gate with applications
IPC: H03K19/00
Filed: 1972-03-15
Abstract: 1366402 Logic circuitry BURROUGHS CORP 16 March 1972 [15 March 1971] 12005/72 Heading G4A An inhibit gate includes a RS flip-flop 1 (Fig. 1), an inhibit signal applied direct to the reset input terminal R preventing the transfer to output terminal 4 of the flip-flop of a binary signal applied direct to the set terminal S and via an inverter 12 to the reset terminal R. The flip-flop comprises OR gates 6, 8 connected to the set and reset input terminals respectively, the output of each gate being connected via inverters 7, 9 to the input of the other gate. The flip-flop output is taken from inverter 9. The circuit may be used in a priority resolver in which each source (21, 22, 23, Fig. 3, not shown) requesting access to utilization means 20, e.g. a random access store, to which it is connected via an associated AND gates (29, 31, 33) and OR gate (37) applies a signal on an associated lead (24, 25, 26) to a priority resolver (27). The lead having highest priority is fed direct to a first flip-flop (40, Fig. 4, not shown) so that the highest priority AND gate (29) is enabled. It is also fed in the inhibit input of flipflops (43, 38) associated with devices of lower priority. The gate may also be used in the computer system of Figs. 6 and 7 (not shown). When one of a plurality of processers and multiplexors (50-55) requires access to one of a plurality of memory modules (56, 57, 58; 59, 60, 61; ... 62, 63, 64) controlled by memory control units (65, 66 ... 67), e.g. if the processor of highest priority (50) requires access to one of the modules (61) controlled by the second control unit (66), an address compare circuit (100) (there being one such compare circuit in each control unit for each processor) examines the address from the processor to give a signal via an AND gate (101) to the set input of a jk flip-flop (104). The resultant output signal is applied to a priority resolver (76) in the module (61) and to AND gates (106, 107, 112). Since the processor has the highest priority its request for access signal is applied via isolation gates to inhibit any other processor requests. If the priority resolver grants access the resulting signal enables AND gates (106, 105) to apply a signal to permit transfer of data from the processor (50) via write circuitry (72) to the memory (86) in the module. Similarly AND gate (108) is enabled to set a flip-flop (110) to enable read circuitry (71) to permit transfer of data to the processor (50) from the memory. The memory includes a register (88) which stores the 14-bit address at which access is required, fed from the processor via fourteen address cross-point units. The first bit of the address from the processor is fed to a gate (29) in the first address module (70), the gate being primed by the output of flip-flop (40) receiving on its set input the access granted signal so that the bit is transferred via a gate (37) to the register (88), the other bits being similarly processed to store the required address in the memory. Each of the address cross point units includes a priority resolver similar to that of Fig. 4.